Wood meal and method of manufacturing the same

ABSTRACT

The present invention relates to wood meal prepared by crushing raw material wood to obtain treated wood meal, pulverizing the treated wood meal under frictional forces of pulverizer balls to obtain wood meal granules with increased bulking density, preparing particles that are finer and harder than said granules, and fixing said finer particles onto the surface of the granules by external pressing force. Said finer particles may also be fixed on said treated wood meal in the process of pulverization to increase the bulking density or on said granules that have been increased of the bulking density. The finer particles may include one or more kinds selected from pigments, electroconductive substances, inorganic substances, plastic materials, and metallic materials.

This is a division of application Ser. No. 08/300,864, filed Sep. 6,1994, which is a continuation of application Ser. No. 07/885,698, filedMay 19, 1992, both abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to wood meal and a method of manufacturingthe same. More particularly, it relates to wood meal which is used as afiller or a coloring agent for plastic moldings, plastic sheets andplastic films, on whose surface are fixed hard particles, and which isused as an electroconductive filler for coatings for such use as amaterial for electromagnetic interference seal, absorbing radio wave andantistatic agent.

2. Description of the Prior Art

In order to obtain various plastic moldings, plastic sheets or plasticfilms (hereinafter referred to generally as plastic products) with theproperties, particularly the surface properties similar to those ofnatural wood, and in order to obtain surface coating material or filmmaterial with such surface properties to be used on furniture and dailyutensils, attempts have been made to add wood meal in the form of veryfine particles to plastic materials or to coating and film materials.

Various products that are given the surface properties similar tonatural wood are preferably colored on the surface in the tone similarto that of wood. It has therefore been the practice in the prior art toadd a given amount of pigment together with a given amount of wood mealwhen plastic products are molded or surface coatings or films areformed.

Description in more detail is given below to wood meal and pigments thatare added and blended in the prior art in plastic products and coatingmaterials as a filler or coloring agent.

In the prior art, wood meal in the form of fine particles is used as afiller to prevent deformation of plastic products during moldingprocess, to give the products desired hardness, and to improve theoverall and relative moisture absorbing/releasing properties.

Attempts have been made in the prior art wood meal to improve itsproperties so that it would not become coagulated during handling, thatit would uniformly disperse in the plastic material, and that it wouldprevent formation of wood vinegar gas during molding process using amolding machine.

A typical example of improved wood meal is the powder obtained bygrinding the surface of particle boards that are hardened with urea baseresin.

The powder obtained by grinding particle boards is used mainly becausethe powder thus obtained comprises very fine "granules" with relativelylittle fluffy fibers. In other words, a powder of very fine and smoothgranules which disperse well in plastic materials for moldings can beobtained if and when appropriate means are used to grind the particleboards.

On the other hand, particle boards from which wood meal is ground lackuniformity in the wood properties, and the wood meal obtained therefromtends to lack properties of a uniform and homogenous wood.

The grinding means such as sand paper to be employed also greatlyaffects the particle size of the resultant ground powder. Hard portionsin the particle board formed by said hardening treatment with urea basedresin become mixed in the ground powder, deteriorating the essentialproperties of wood meal such as moisture absorbing or releasingproperties and soft texture.

It has therefore been proposed in the prior art to subject the startingmaterial wood not only to mechanical pulverization using a cutter millbut to a pulverizer that utilizes impact, shear and friction forces suchas an impeller mill in order to preserve the intrinsic properties of thematerial wood such as moisture absorbing and releasing properties.

A reference will now be made to pigments that are used as a coloringagent for plastic products and resin coatings.

Generally, pigments come in fine powder of inorganic or organicmaterial, and are used as a coloring agent and an extender for plasticproducts and coatings.

When used as a coloring agent for plastic products, such pigments mustbe heat resistant insoluble in solvents, and effectively dispersed inthe molding material.

When used in coating solutions, said pigments must be well dispersed inthe coating solution without coagulating and without becoming settled inthe solution.

When used in coatings made of powder such as powder of epoxy resin, thepigments must have a good flowability to be well blended with the resinpowder.

Fine powders of metals such as Ag, Cu and Ni and of metallic oxides suchas SnO₂ and ZnO and carboll powders have been used as a filler forcoatings to give electroconductive properties such as forelectromagnetic shielding, absorbing radio waves, and antistatic agent.Such conductive fillers must be uniformly dispersed in the coatingsolution such as of resin.

Fine powders of inorganic material such as of calcium carbonate wereused as a filler for plastic products to give dimensional stability andsurface hardness required of plastic products.

These various aspects of the prior art entailed the following problems.

Firstly, the ground powder of particle boards failed to give sufficientand uniformly distributed moisture absorbing property to plasticproducts when the powder was blended and dispersed in the starting resinmaterial for molding the plastic products, or when blended and dispersedin resin coatings. Rather, the powder tended to give sticky feel on thesurface of the resultant product or coating.

Hard particles of thermosetting resin contained in the ground powderobtained from particle boards become exposed on the surface of theplastic products or coatings, deteriorating the intrinsic soft textureof a wood material.

Wood meal obtained by pulverizing wood material with a pulverizer thatutilizes impact, shear and friction forces such as an impeller mill mayretain various properties intrinsic and unique to a wood material, butits particles are fluffy and often include elongated and fibrousparticles. Such wood meal is extremely inferior in its dispersingproperty when blended in a coating solution, nor does it disperseuniformly in various resin materials for molding plastic products or infillers. The wood meal obtained as above easily becomes coagulatedduring pulverization or during storage, posing problems in handling. Italso poses problems as it easily becomes coagulated in the resinmaterial for plastic products or in the coating solutions.

When wood chips and the like are directly pulverized in a dry ball millto obtain wood meal, the amount of resultant wood meal obtained by onecycle of pulverization is extremely small. What is more, despiteprolonged pulverization, a large amount of particles with long fiberswould still remain in the resultant powder, while at the same time, alarge amount of over-pulverized particles is produced. Theover-pulverized particles pose problems when in use as they easilybecome coagulated with one another.

As for the pigments used as a coloring agent, the particle size isgenerally very small, measuring about 1 μm. Particularly in the case ofan organic pigment, the primary particle size ranges between 0.1 μm and0.5 μm. These extremely small particles of pigment do not disperseuniformly when blended in resin materials for molding or coating, andwill not give sufficient coloring commensurate with the pigmentaddition. Particles of pigment easily become coagulated, and coagulatedparticles of pigment tend to deteriorate the surface properties of theplastic products to thereby cause uneven coloring.

Particles of pigment do not disperse uniformly in coating solutions orsolvents, as mentioned earlier. They tend to become settled in thesolvent or coating solution as time elapses, again failing to givesufficient coloring on the surface commensurate with the amount ofpigment addition. As also said earlier, particles of pigment easilybecome coagulated with one another, deteriorating the surface propertiesof the coating to thereby cause uneven coloring.

Pigments of extremely small particles lack flowability, and when blendedwith a powder coating material such as epoxy resin powder, pigmentparticles tend to form lumps instead of being well blended.

As for the powders to be used as an electroconductive filler, theparticles are selected within the size range of several microns and aredirectly blended and dispersed in a coating solution. Fine particles ofconductive filler are also defective in that they easily becomecoagulated during storage, handling, addition or blending, hamperinguniform dispersion.

As a result, lumps of filler particles become exposed on the surface ofthe coating layer, forming wavy or irregular surface, cuts or openings,and deteriorating the adhesion, heat resistance or weatherability of thecoating layer.

Because of relatively heavy weight for their small particle size,particles of conductive fillers tend to become settled in the coatingsolution with time, resulting in uneven distribution within the solutionand impairing homogeneity of the coating layer to be formed.

Electroconductivity of the coating layer itself formed by addition ofthe conductivy filler is greatly affected by the electric coupling ofthe conductive particles contained. The smaller the particle size, thehigher the required ratio of conductive particle addition, and theadhesion and elasticity of the coating layer deteriorate in proportionto the level of conductivity.

Calcium carbonate powder used as a filler for plastic products does notdisperse well in the resin material, and often becomes settled in thesolvent or coating solution when blended and dispersed therein.Properties of the resultant plastic product may vary within the product,failing to give dimensional stability and surface hardness of a desiredlevel.

OBJECT OF THE INVENTION

A primary object of the present invention is to provide wood meal whichhas excellent and increased flowability and dispersion property whenblended in the resin material for molding plastic products, which allowsharder particles to be fixed on the surface, and which has a higherperformance as a barrier both on the inside and outside, and a methodfor manufacturing the same.

A second object of this invention is to provide wood meal whichmaintains various properties and functions intrinsic in the startingwood material, and on whose surface are fixed finer particles havingvarious functions such as particles of pigments, electroconductivematerial, inorganic material, metals and plastics, and a method formanufacturing the same.

A third object of this invention is to provide particles of wood meal ofa higher bulking density and on whose surface are securely and uniformlyfixed finer particles having various functions, and a method formanufacturing the same.

A fourth object of this invention is to provide particles of wood mealwherein said finer particles having various functions are constantlyfixed on the surface of each particle in a thermally and chemicallystable manner, and a method for manufacturing the same.

A fifth object of this invention is to provide particles of wood mealwhich effectively support various pigments to achieve excellent coloringeffect, and which have excellent flowability and dispersion propertywhen blended and dispersed in a resin material or coating material, anda method for manufacturing the same.

A sixth object of this invention is to provide particles of wood mealwhich can be well dispersed in the coating material, and whose surfaceproperties are modified to give excellent conductivity to the coatinglayer formed using the wood meal.

A seventh object of this invention is to provide particles of wood mealwhich effectively support various inorganic particles to be used as afiller, which do not become coagulated during processing, handling andstorage or when blended and dispersed in the resin material for moldingor coating, and which have excellent flowability and dispersion propertyto constantly remain well blended and dispersed in the resin material,and a method for manufacturing the same.

These and other objects of the present invention will become apparentfrom the following description.

SUMMARY OF THE INVENTION

To achieve these objects, the wood me&l and its manufacturing methodwill be described.

The wood meal according to the first invention is obtained by crushingthe raw material wood, further pulverizing the crushed wood meal underthe frictional forces of pulverizer balls to increase the bulkingdensity, and fixing the surface of thus obtained wood meal with pluralparticles that are harder and smaller than the wood meal particles by anexternal pressing force.

The first invention is characterized in that said plural finer particlesare fixed on the surface of the wood meal by an external pressing forceas these particles bite into the surface.

The first invention is further characterized in that said finerparticles are fixed on the surface of the wood meal by at least one ormore of the following means: the surface of the wood meal embracing thefiner particles, including the form of said biting of the particlesthemselves; the finer particles biting into the surface becomingentangled with one another; or, one or more of the particles bit intothe surface becoming entangled with one or more particles that areembraced in the surface of the wood meal.

The first invention is also characterized in that said plural particlesto be fixed on the surface of the wood meal having a higher bulkingdensity are mainly particles of pigment or conductive material that aresmaller and harder than the wood meal particles.

Said plural particles may be of any inorganic, plastic or metallicmaterial.

Said plural particles are two or more of the kinds selected frompigments, conductive materials, inorganic substances, plastics andmetals.

The second invention is characterized in that the treated wood mealobtained by crushing the raw material wood is further subjected topulverization under the frictional forces of pulverizer balls toincrease the bulking density while plural particles which are smallerand harder than particles of the wood meal of a higher bulking densityare fixed on the surface of the treated wood meal by an externalpressing force.

The second invention is also characterized in that said finer particlesare fixed on the surface of the treated wood meal as the former biteinto the surface of the latter.

It is further characterized in that said finer particles are fixed onthe treated wood meal surface by at least one of the following means:the surface of the treated wood meal embracing the finer particles,including biting of said particles themselves; the finer particlesbiting into the surface becoming entangled with one another; or, one ormore of the particles bit into the surface of the wood meal becomingentangled with one or more particles embraced in the surface.

The second invention is further characterized in that said finerparticles to be fixed on the surface of the wood meal being treated tohave or having a higher bulking density are mainly particles of pigmentor conductive material that are smaller and harder than the wood mealparticles.

Said finer particles may be of any inorganic, plastic or metallicmaterial.

Said finer particles are two or more of the kinds selected frompigments, conductive materials, inorganic substances, plastics andmetals.

The third invention relates to a method for manufacturing wood mealwhich comprises at least the steps of crushing the raw material wood,further pulverizing the wood meal thus obtained under the frictionalforces of pulverizer balls to increase the bulking density, preparingfiner particles that are harder and smaller than the wood mealparticles, and fixing said finer particles on the surface of the woodmeal by an external pressing force.

The third invention is characterized in that in the method formanufacturing wood meal having a higher bulking density, said finerparticles are fixed on the wood meal surface by the biting force of theformer.

The third invention is further characterized in that said finerparticles are fixed on the surface of the wood meal having a higherbulking density by at least one of the following means: the surface ofthe wood meal embracing the finer particles, including biting of saidparticles themselves; the finer particles biting into the surfacebecoming entangled with one another; or, one or more of the particlesbit into the surface becoming entangled with one or more particlesembraced in the surface of the wood meal.

The third invention is also characterized in that said finer particlesto be fixed on the surface of the wood meal having a higher bulkingdensity are mainly particles of pigment or conductive material that aresmaller and harder than the wood meal particle.

Said plural particles may be of any inorganic, plastic or metallicmaterial.

Said finer particles are two or more of the kinds selected frompigments, conductive materials, inorganic substances, plastics andmetals.

The fourth invention relates to a method for manufacturing wood mealcomprising at least the steps of preparing treated wood meal by crushingthe raw material wood, preparing particles that are smaller and harderthan the treated wood meal particle, charging said treated wood meal andsaid finer particles to pulverize the former under the frictional forcesof pulverizer balls to increase the bulking density while causing thelatter particles to be fixed on the surface of the former by an externalpressing force.

The fourth invention is characterized in that said wood meal obtained bycrushing the raw material wood is further treated to have a higherbulking density under the frictional forces of pulverizer balls, and thefiner particles are charged by first sprinkling the latter over theformer to cover the surface of the former.

The treated wood meal and the finer particles may be charged separatelyor simultaneously.

The fourth invention is characterized in that in the method ofmanufacturing wood meal by pulverizing said treated wood meal by thefrictional forces of pulverizer balls to increase the bulking densitywhile the finer particles are fixed on the surface of the treated woodmeal or the wood meal having a higher bulking density, the particles ofthe smaller size are fixed on the surface of the treated wood meal bythe biting force of the former.

The fourth invention is further characterized in that said pluralparticles are fixed on the surface Of the wood meal be at least one ofthe following means: the surface of the wood meal embracing the finerparticles, including biting of said particles themselves; the finerparticles biting into the surface becoming entangled with one another;or, one or more of the particles bit into the surface of the wood mealbecoming entangled with one or more particles embraced in the surface.

The fourth invention is also characterized in that in the method ofmanufacturing wood meal by pulverizing said treated wood meal by thefrictional forces of pulverizer balls to increase the bulking densitywhile the finer particles are fixed on the surface of the treated woodmeal or the wood meal having a higher bulking density, said pluralparticles that are smaller and harder than said wood meal particlehaving the increased bulking density are mainly particles Of pigments orconductive material.

Said plural particles may be of any inorganic, plastic or metallicmaterial.

Said plural particles may be two or more of the kinds selected frompigments, conductive materials, inorganic substances, plastics andmetals.

It should be noted that said second invention may include the case wheresaid crushed wood meal is being treated to increase its bulking densityunder the frictional forces of pulverizer balls while said particles ofthe smaller size are permanently or temporarily fixed on the surface ofthe former, and the case where said crushed wood meal is treated toincrease its bulking density and then said particles of the smaller sizeare fixed thereon.

It is also noted that according to the fourth invention, the particlesof the smaller size may be permanently or temporarily fixed on thesurface of the crushed wood meal while or after the latter is treated toincrease its bulking density, or may be fixed on the wood meal surfacebefore the latter is treated to increase its bulking density under thefrictional forces of pulverizer balls.

Therefore, according to any one of the first through fourth inventions,the wood meal obtained by crushing the raw material wood may bepulverized under the frictional forces of pulverizer balls to increaseits density before (first, second, third and fourth inventions), ordepending on the circumstance, after said particles of the smaller sizeare partly fixed on the surface of the former (the second and fourthinventions).

Because the matrix on which the finer particles are fixed is the woodmeal which is treated to increase its bulking density or which partlycontains particles so treated, the matrix itself retains variousproperties and functions of a wood material.

Moreover, the finer particles cover or substantially cover the surfaceof the matrix wood meal, forming a barrier on said surface andmaterially and effectively preserving the properties of the wood meal.

At the same time, excellent flowability and dispersion performanceessential to a filler are given to the wood meal.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be made to the following detailed description, taken inconnection with the accompanying drawings, in which:

FIG. 1 is a schematic diagram to show example processes of preparingtreated wood meal from a raw material wood and fixing plural finerparticles on the surface of the treated wood meal, preparing wood mealparticles from the treated wood meal and fixing plural particles on thesurface of the treated wood meal, and the first and the second woodmeals thus structured;

FIG. 2 is a vertical front section to show the diagrammatic structure ofthe essential part of an open type dry ball mill for pulverizing thewood meal utilizing the frictional forces of pulverizer balls accordingto the present invention;

FIG. 3 is a vertical front section to show the diagrammatic structure ofthe essential part of a closed type dry ball mill for pulverizing thetreated wood meal and wood meal granules utilizing the frictional forcesof pulverizer balls according to the present invention;

FIG. 4 is a vertical front section to show the diagrammatic structure ofthe essential part of an apparatus for classifying the treated wood mealand wood meal granules according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention wood meal and the method for manufacturing thesame will now be described in more detail.

Before going into the details, essential terms used in the descriptionwill be defined. It should be understood that because of particularnature and size of the wood meal which is the subject matter of thisinvention, we are obliged to estimate its properties and effects to someextent, and that the present invention is not necessarily limited by thefollowing definition: "pulverization under the frictional forces ofpulverizer balls" means, for example, pulverization of particles mainlyutilizing the frictional forces of a ball mill (hereinafter alsoreferred to as "frictional crushing"). "Ball mill" mainly means a rotarymill such as a ball mill in which pulverizer balls are vertically aswell as circumferentially agitated by an agitating means to causefrictional forces among the balls for pulverization. "Wood mealparticles" generally means the treated wood meal whose bulking densityis increased by pulverization under the frictional forces of pulverizerballs, in particular the rugged edges, protruding portions andvilus-like fibers of said treated wood meal are altered by thepulverization by the frictional forces of the balls to thereby result inan increased bulking density. It is therefore noted that "wood mealparticles" herein generally have irregular contours including, but notlimited to, spherical and quasi spherical particles. Here, "wood mealparticles" having increased bulking density generally means wood mealwhose bulking density is substantially increased by the pulverization oftreated wood meal under the frictional forces of pulverizer balls, andmay include not only wood meal whose bulking density is increased by thepulverization under the frictional forces of pulverizer ballsirrespective of the fixing of the particles on the surface, but alsowood meal whose bulking density is substantially increased by thepulverization under the frictional forces of pulverizer balls while saidfixing of the particles on the surface is being conducted and wood mealwhose bulking density is increased by the pulverization after saidfixing of the particles on the surface is conducted.

It is noted that the bulking density can be increased by substantiallyshaping the contour of the treated wood meal by pulverization under thefrictional forces of pulverizer balls.

The bulking density of the treated wood meal is increased by thefollowing steps: relatively elongated and fibrous particles of wood mealare crushed by the friction of the balls in the pulverizer to be shapedmore like granules; rugged edges of granules are rounded by the frictionof the balls; protruding portions are rounded by the friction of theballs; vilus-like fibers are removed by the friction of the balls;and/or, portions with lower density lowered by entanglement ofvilus-like fibers are increased in density by the friction of the balls.

"External pressing force" means herein external pressing force exertedon the wood meal surface mainly by a mechanical means such as saidfrictional crushing force which is generated as a result of compressionor pressing force as a result of pulverization.

"Fixing" means that the finer particles are attached on the wood mealsurface without resorting to any chemical reaction or an adhesive, anddo not easily become detached.

The particle size of the treated wood meal and the wood meal granules(Tables 2, 3, 4, 5, 6 and 7) means a value which is obtained by passinga solution containing either said treated wood meal or wood mealgranules suspended/dispersed therein through a transparent flow path,irradiating laser beams onto the flow path, measuring the length in thedirection of flow, and converting the value thus measured into adiameter.

The particle size of the raw material wood (Table 1) is measured bysifting the raw material wood with a test vibrating screens (Ro-tapshaker) for five minutes. The value indicates the mesh size of the finerscreen through which the raw material wood did not pass.

"Mean particle size" means the particle size of the treated wood meal orwood meal granules weighing 50 wt % (half the entire volume) incumulative weight percent distribution.

"Hardness" means the hardness of the starting raw material beforepulverization such as the shore hardness, since, as mentioned earlier,the treated wood meal, wood meal granules or the finer particles to befixed on the wood meal surface are relatively small in size and aretherefore difficult to directly measure their hardness.

The first and second wood means according to one example are morespecifically described referring to FIG. 1.

The first and the third inventions are more specifically described bythe example of the first wood meal and the method for manufacturing thesame.

The second and fourth inventions are more specifically described by theexample describing the second wood meal and the method for manufacturingthe same.

The first wood meal according to the example is obtained by pulverizinga large amount of said treated wood meal by the frictional forces of theballs to shape the outer contour to thereby increase the bulking densityand then by fixing on the surface thereof particles that are harder andsmaller than said treated wood meal.

The second wood meal according to the example is obtained by pulverizinga large amount of treated wood meal and said particles of the smallersize by the friction forces of the balls while the latter particles areconcurrently fixed on the surface of the former. Said particles of thesmaller size may first be fixed on the surface of the treated wood mealbefore the bulking density of the treated wood meal is increased bypulverization under the frictional forces.

First Wood Meal

A typical first and a second methods for obtaining the first wood meal110 will now be described.

A typical first method for obtaining the first wood meal 110 is shown by[A] in FIG. 1.

According to the first method, raw material wood 101 is first crushed bya pulverizer which operates by the forces of impact, shear and frictionto obtain treated wood meal 102 having the size within a given range.

The surface of the treated wood meal 102 is shaped by pulverizationunder the frictional forces of the balls to obtain wood meal granules111 with an increased bulking density.

The wood meal granules 111 thus obtained and separately prepared fineparticles 112 are charged into a pressurizing means such as dry ballmill which generates external pressing force to fix the fine particles112 onto the surface of the granules 111, to thereby obtain the firstwood meal 110.

The typical second method for obtaining the first wood meal 110 is shownby [B] in FIG. 1.

According to the second method, the wood meal granules 111 obtained bythe first method are sprinkled with the fine particles 112 or otherwiseadhered thereto by way of preliminary mixing. The granules 111 coveredwith the fine particles 112 are charged in a pressurizing means such asa dry ball mill to fix the fine particles by external pressing forceexerted by said means, to thereby obtain the wood meal 110.

Whereupon, the wood meal granules 111 with an increased bulking densitywhich are obtained by mechanically crushing the treated wood meal 102have a more perfect shape as the treated wood meal 102 having somewhatelongated and fibrous shape is broken into smaller pieces by saidcrushing process. Rugged edges and protruding portions of the wood meal102 are rounded and vilus-like fibers are removed.

Because of the increased bulking density, the granules 111 can be moreeasily processed to have the fine particles 112 fixed on the surfacethereof while retaining various properties and functions such asmoisture absorbing and releasing performances and soft texture that arepeculiar to the raw material wood 101.

Fine particles 112 are therefore more uniformly and easily fixed on thesurface of granules 111 of the wood meal 110 by the external pressingforce.

As the fine particles 112 bite into the surface of the first wood meal110 thus obtained to increase the bulking density of the granules 111,the fine particles 112 remain more firmly and uniformly fixed on thesurface of the latter.

Because the granules 111 constituting the wood meal 110 have anincreased bulking density and because the fine particles 112 are fixedon the surface of the granules 111, the resultant wood meal 110 has anexcellent flowability, preventing its Coagulation during handling. Thewood meal 110 has a good dispersion performance when blended with othercompounds such as coating material.

Because the fine particles 112 are fixed on the surface of the granules111 merely by the external pressing force, the fine particles 112 willnot become separated from the granules 111 even when the granules areused in a solution or solvent, and at high temperatures.

Because various properties and functions of the fine particles 112 canbe manifested while the particles 112 are being fixed on the surface ofthe first wood meal 110, handling of the particles in this state is mucheasier than the particles not fixed on the granules 111.

Because the fine particles 112 of the first wood meal 110 cover orsubstantially cover the surface of the matrix granules 111 to form abarrier thereon, seepage of wood vinegar or lignin from within thegranules 111 can be prevented. This barrier also acts to improve theresistance to external heat, to prevent infiltration of undesirablechemicals and to adequately protect the wood meal granules 111, so thatthe properties of the resultant wood meal 110 can be fully exhibited.

Because the granules 111 constituting the first wood meal 110 arecovered with the fine particles 112, the granules 111 that areintrinsically low in hardness or strength and in specific gravity arecompensated and protected by the high hardness and high specific gravityof the fine particles 112.

Because the granules 111 are relatively light in weight, the weight ofthe wood meal as a whole can be reduced. What is more, wood remnantsthat were heretofore not fully utilized can be effectively used,contributing to preservation of resources.

The granules 111 of the wood meal 110 and the powder of titanium oxidewhich is used as the fine particles 112 to be fixed on the surface ofthe granules 111 may have the following particle size distribution,provided that the powder of titanium oxide is also subjected topulverization at the time of fixing thereof.

    ______________________________________                                        Particle Size Distribution                                                    wood meal granules                                                                          (as against)                                                                            titanium oxide powder                                 ______________________________________                                         1-10 μm             0.2-3 μm                                           11-30 μm               1-5 μm                                           ______________________________________                                    

The hardness of the raw material wood 101 for obtaining the granules 111and of the fine particles 112 such as titanium oxide, carbon, nickel andcalcium carbonate is shown below in terms of Shore hardness which ismeasured by the height of rebound hammer dropped from a given height.

    ______________________________________                                        Raw material wood     35-50                                                   Titanium oxide        150-180                                                 Carbon                60-65                                                   Nickel                90-100                                                  Calcium carbonate     120-140                                                 ______________________________________                                    

Second Wood Meal

A typical first method for manufacturing the second wood meal is shownby [C] in FIG. 1.

According to the first method, raw material wood 101 is first crushed bya pulverizer which operates by the forces of impact, shear and frictionto obtain treated wood meal 102 having the granule size distributionwithin a given range.

The wood meal 102 thus treated and fine particles 122 are charged in thepulverization unit which operates by the frictional force of the ballsto increase the bulking density of the wood meal 102 per se while saidfine particles 122 are being fixed on the surface of the treated woodmeal 102, the wood meal 102 on its way to be pulverized into thegranules 121, or the granules 121 whose bulking density is beingincreased by said pulverization process. The fixing is also effected bythe frictional forces of the balls.

Pulverization under the frictional forces of the balls is continueduntil said treated wood meal 102 is sufficiently pulverized intogranules 121 with an increased bulking density.

The second wood meal 120 is obtained by the above mentioned processes.

A second method for obtaining the second wood meal 120 is shown by [D]in FIG. 1.

According to the second method, the treated wood meal 102 obtained bythe same means as, used in the first method is shrinkled with the fineparticles 122 of otherwise adhered with the particles 122 by way ofpreliminary mixing. The treated wood meal 102 covered with the fineparticles 122 is subjected to pulverization under the frictional forcesof the balls.

Pulverization of the wood meal 102 under the frictional forces of theballs is continued until the wood meal 102 is sufficiently pulverizedinto granules 121 with sufficiently high bulking density, and also untilthe fine particles 122 are firmly fixed on the surface of the granules121 that are formed by this pulverization under the frictional forces ofthe balls.

The second wood meal 120 is thus obtained.

In the course of pulverization under the frictional forces of the balls,the outer surface and the contour of the treated wood meal 102 undergochanges and become substantially shaped.

This shaping is also achieved both when the wood meal 102 and the fineparticles 122 are simultaneously charged in a pulverizer, and when thewood meal 102 which is sprinkled with the fine particles 122 is charged,with the wood meal 102 being shaped in one way or the other to beincreased in the bulking density.

In other words, the surface of the wood meal 102 can be adequatelyshaped by the pulverization process conducted prior to fixing of thefine particles 122, by the external pressing force at the time of fixingthe fine particles 122, and by the abrasive force applied on the fineparticles 122 after they are fixed on the surface.

More specifically, the treated wood meal 102 can be more adequatelyshaped by the frictional forces of the balls as the elongated andfibrous granules are cut into smaller pieces.

Rugged edges and protruding portions of the treated wood meal are alsorounded by the frictional forces of the balls and better shaped as agranule.

Vilus-like fibers of the wood meal 102 are eliminated as the fineparticles 122 cover the peripheral surface of the wood meal 102, or asthe portions of the vilus-like fibers which protrude beyond the fineparticles 122 are cut by the abrasion.

The surface of the treated wood meal 102 is shaped by the frictionalforces of the pressing and rotating balls.

The second wood meal 120 thus obtained provides wood meal granules 121having an increased bulking density as the wood meal 120 is pulverizedunder the frictional forces of the balls. Because the fine particles 122are fixed on the surface of the granules 121 with an increased bulkingdensity, the fine particles 122 are securely and uniformly held fixed.

The resultant wood meal 120 has sufficient flowability so that the woodmeal 120 itself does not become coagulated during its handling, assuringgood dispersion when blended in other compounds.

The fine particles 122 on the surface of the second wood meal 120 arefirmly fixed on the surface of each granule 121. Because the fixing iseffected by the external pressing force alone, the fine particles 122will not become separated from the surface of the granules 121 even whenthe wood meal 120 is used in a solution or solvent and at hightemperatures. The fine particles are securely held fixed on the surfaceof the granules 121.

Because various properties and functions of the fine particles 122 onthe surface of the second wood meal 120 can be manifested while theparticles 122 are being fixed on the surface of the second wood meal110, the fine particles 122 can always be used without becomingcoagulated.

Because the second wood meal 120 is obtained by mechanically crushingthe raw material wood 101, it retains the unique properties andfunctions such as moisture absorbing and releasing performances and softtexture of the raw material wood 101 itself. What is more, because thefine particles 122 cover or substantially cover the surface of thegranules 121 to form a barrier thereon, various properties andperformances of the raw material wood 101 are effectively maintained inthe wood meal 120.

Manufacturing Means for the 1st and 2nd Wood Meals

Details of the manufacturing means for the first and second wood meals110 and 120 will now be described.

The wood meal 102 to be treated to obtain the second wood meal 120corresponds in substance to the wood meal 102 to be treated to obtainthe first wood meal 110.

As for the first and second wood meals 110 and 120 respectively, thetreated wood meal 102 used in the process of preparing the second woodmeal 120 substantially corresponds with the treated wood meal 102 usedas the material for the first wood meal 110.

The means and mode of fixing plural fine particles 122 on the surface ofthe second wood meal 120 are also substantially the same as those usedfor the first wood meal 110.

Therefore, description will be made mainly with respect to the firstwood meal 110, with references made to the second wood meal 120 whenevernecessary.

As the raw material to be crushed to obtain the wood meal, anyconiferous and broad-leaved wood materials for general use may be usedin the form of logs, chips or sawdust.

The raw material wood 101 is subjected to a known mechanical means suchas a cutter mill to be cut and crushed to a particle size of smallerthan 1000 μm, preferably smaller than 500 μm without impairing itsproperties and functions as a wood material.

The raw material wood 101 is also subjected to pre-treatments ifnecessary. Such pre-treatments include removal of substances such aslignin and tannin, coloring matter, resins or other undesirable mattersused for bleaching or other purposes and may be conducted using knownmeans.

Subsequently, the wood material 101 is pulverized using a pulverizerthat operates by the forces of impact, shear or friction such as animpeller mill without impairing the properties and functions of a woodmaterial to obtain treated wood meal 102 with the particle size ofpreferably smaller than about 200 μm.

As mentioned earlier, the treated wood meal 102 contains elongatedparticles with vilus-like fibers on the surfaces although it maintainsvarious properties and functions intrinsic to a wood material.

Particles of the wood meal 102 are generally rather massive, rugged andirregular in shape. They tend to become coagulated with one another.

The pulverizer to be used in the present invention may be an impellermill which comprises impellers provided radially on a rotor, theclearance between the impellers and the corrugated liner inside thepulverizer being adjustable.

By rotating the rotor at a high speed while adjusting the clearance ofthe impeller mill, the wood material 101 is crushed under the impact ofthe impellers and the liner. The impellers themselves press the woodmaterial against the liner to promote pulverization of the treated woodmeal 102.

Although the wood meal 102 thus pulverized may be used withoutclassifying the particles, it is preferable to classify the particlesduring or after pulverization to have uniform particle distribution inthe treated wood meal 102.

Prior to or during the subsequent pulverization under frictional forces,the wood meal 102 is dried to contain less than 10 wt %, preferably lessthan 8 wt % and still more preferably less than 3 wt % of moisture.

The wood meal 102 is dried for the purposes of facilitating shaping ofthe particle surface by the pulverization, and preventing adverseeffects on the substances such as Plastic products and coating materialsto which the wood meal 102 is blended.

Then, the wood meal 102 is subjected to mechanical pulverization using ameans which utilizes the frictional forces of the balls. In the case ofthe first wood meal, pulverization is conducted before the fineparticles 112 are fixed on the surface. In the case of the second woodmeal, pulverization is conducted simultaneously with or prior topermanently or temporarily fixing the fine particles 122 on the surface.

A dry ball mill shown in FIG. 2 is typically used for this mechanicalpulverization. The pulverization with the dry ball mill is describedwith respect to the formation of wood meal granules 111 of the firstwood meal 110.

During pulverization of the wood meal 102 in the dry ball mill, rapidrise of the temperature in the mill leading to a violent explosion isanticipated. It is also feared that the properties and functions of thewood meal itself or its granules having an increased bulking density maybe impaired by the high temperature of the mill. A cooling jacket 2 istherefore provided to surround the mill 1, as shown in FIG. 2, toconstantly circulate cooling water from a water supply pipe 8 to anexhaust pipe 9 to thereby maintain the mill at least at 80° C. or below,preferably below 70° C.

Inside the mill are provided an agitating bar 4 and plural balls 3 thatare agitated and rolled by the bar 4. The wood meal 102 is charged fromthe open top and discharged from an outlet port 7 via an exit valve 6after processing. The ball mill is of so called batch system.

The balls 3 which exert frictional forces on the wood meal are ceramicballs of 3-15 mm diameter. Use of stainless steel balls is avoided infear of potential explosion.

The wood meal 102 charged in the dry ball mill is subjected tofrictional forces of the rolling balls 3, whereby elongated particlesare broken into still smaller pieces, rugged or protruding portions ofthe particles are rounded, and vilus-like fibers are removed. Because ofthe frictional heat generated by the friction among the rolling balls orbetween the balls and the wood meal, the wood meal is rapidly heated toa temperature high enough to replace the moisture. As a result ofcontinued pulverization, the moisture content of the wood meal will bereduced to 3-5 wt %.

The wood meal 102 tends to somewhat shrink due to drying, which in turnfacilitates biting of the fine particles fixed on the surface during thefixing process in the subsequent step.

As shown in FIG. 3, a closed type dry ball mill comprising a lid 10, anexhaust air pipe 11, and an air supply pipe 12 may also be used.

In the case the closed type ball mill is used, the oxygen level insidethe mill is preferably maintained below 15% and the temperature below80° C. After the mill is closed with the lid 10, the air inside the millis replaced with an inert gas such as nitrogen gas via the exhaust pipe11 and the air supply pipe 12; alternatively, nitrogen gas iscontinuously supplied, and pulverization is conducted in an inertatmosphere.

The wood meal granules 111 thus pulverized, shaped and increased of thebulking density may be classified using a classifier such as shown inFIG. 4.

The classifier is a device for air classification by the true specificgravity. The granules are supplied in the direction of arrow Y.

The granules 111 were classified in the classifier where the centrifugalforce generated by the rotation of a classifier rotor 13 driven by amotor 14 balances with the vacuum force acting in the direction of arrowY. Coarse granules that are rejected as not satisfying theclassification conditions are taken out in the direction of arrow X. Theclassifier is also operated in an inert atmosphere as nitrogen gas isalso continuously supplied into the classifier in the direction of arrowN to maintain the oxygen level therein at less than 15% and to avoidviolent explosion of the granules.

The resultant granules 111 are slightly smaller in the mean size andgreater in the bulking density than the wood meal 102, and the elongatedgranules, rugged edges or protruding granules, granules havingvilus-like fibers, and granules sparsely covered with the fine particlesare all rounded, shaped and fully covered.

Experimental examples and comparative examples of the method formanufacturing the wood meal granules 111 will now be described. (Tofacilitate understanding of the experimental and comparative examples,the same reference numbers are used as in the foregoing description,such as the raw material 101, the treated wood meal 102, wood mealparticles 111 and wood meal 110.)

Experimental Example A-I

Chips of black spruce having the particle distribution as shown in Table1 were used as the raw material wood 101, which were subjected tomechanical crushing under the impact, shear or friction of an impellermill (Model IMP-250 manufactured by Seishin Kigyo K. K.) in which theclearance between the impellers of the rotor and the liner was set at 3mm, to obtain treated wood meal 102 having the particle sizedistribution as shown in Table 2.

                  TABLE 1                                                         ______________________________________                                        Particle Size (μm)                                                                      Amount of Distribution (wt %)                                    ______________________________________                                        ˜  297     2.33                                                         297 ˜                                                                            350     2.29                                                         350 ˜                                                                            420     7.21                                                         420 ˜                                                                            500     33.44                                                        500 ˜                                                                            590     40.98                                                        590 ˜                                                                            710     12.78                                                        710 ˜                                                                            840     0.65                                                         840 ˜                                                                            1190    0.32                                                         1190 ˜     0.00                                                         ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Particle Size (μm)                                                                      Amount of Distribution (wt %)                                    ______________________________________                                        0.0 ˜                                                                            0.2     0.0                                                          0.2 ˜                                                                            0.4     0.1                                                          0.4 ˜                                                                            0.6     0.1                                                          0.6 ˜                                                                            0.8     0.1                                                          0.8 ˜                                                                            1.0     0.1                                                          1.0 ˜                                                                            1.5     0.4                                                          1.5 ˜                                                                            2.0     0.7                                                          2.0 ˜                                                                            3.0     1.2                                                          3.0 ˜                                                                            4.0     0.9                                                          4.0 ˜                                                                            6.0     1.5                                                          6.0 ˜                                                                            8.0     2.2                                                          8.0 ˜                                                                            12.0    4.1                                                          12.0 ˜                                                                           16.0    4.0                                                          16.0 ˜                                                                           24.0    7.8                                                          24.0 ˜                                                                           32.0    8.2                                                          32.0 ˜                                                                           48.0    14.2                                                         48.0 ˜                                                                           64.0    10.5                                                         64.0 ˜                                                                           96.0    31.2                                                         96.0 ˜                                                                           128.0   11.0                                                         128.0 ˜                                                                          192.0   1.7                                                          ______________________________________                                    

The wood meal 102 thus crushed was classified using a device for airclassification with specific gravity (PS Separator by Pautech K. K.) toobtain the treated wood meal 102 having the size distribution as shownin Table 3. The wood meal 102 thus crushed and classified was charged ina 5.4 liters capacity dry ball mill (Atritor A-200 manufactured byMitsui Miike Kakouki K. K.) provided with an agitating bar andcontaining 2.4 liters of 3 mmφ ceramic balls and subjected topulverization for two hours to obtain-wood meal granules 111 with anincreased bulking density having the size distribution as shown in Table4.

                  TABLE 3                                                         ______________________________________                                        Particle Size (μm)                                                                      Amount of Distribution (wt %)                                    ______________________________________                                        0.0 ˜                                                                            0.2     0.0                                                          0.2 ˜                                                                            0.4     0.3                                                          0.4 ˜                                                                            0.6     0.4                                                          0.6 ˜                                                                            0.8     0.7                                                          0.8 ˜                                                                            1.0     0.9                                                          1.0 ˜                                                                            1.5     2.9                                                          1.5 ˜                                                                            2.0     5.9                                                          2.0 ˜                                                                            3.0     14.3                                                         3.0 ˜                                                                            4.0     15.0                                                         4.0 ˜                                                                            6.0     16.5                                                         6.0 ˜                                                                            8.0     11.2                                                         8.0 ˜                                                                            12.0    12.1                                                         12.0 ˜                                                                           16.0    7.9                                                          16.0 ˜                                                                           24.0    6.3                                                          24.0 ˜                                                                           32.0    3.1                                                          32.0 ˜                                                                           48.0    0.8                                                          48.0 ˜                                                                           64.0    0.0                                                          64.0 ˜                                                                           96.0    1.7                                                          ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        Particle Size (μm)                                                                      Amount of Distribution (wt %)                                    ______________________________________                                        ˜  0.2     0.0                                                          0.2 ˜                                                                            0.4     0.3                                                          0.4 ˜                                                                            0.6     0.6                                                          0.6 ˜                                                                            0.8     1.0                                                          0.8 ˜                                                                            1.0     1.3                                                          1.0 ˜                                                                            1.5     4.5                                                          1.5 ˜                                                                            2.0     8.1                                                          2.0 ˜                                                                            3.0     14.6                                                         3.0 ˜                                                                            4.0     13.0                                                         4.0 ˜                                                                            6.0     13.5                                                         6.0 ˜                                                                            8.0     13.0                                                         8.0 ˜                                                                            12.0    12.0                                                         12.0 ˜                                                                           16.0    10.9                                                         16.0 ˜                                                                           24.0    6.6                                                          24.0 ˜                                                                           32.0    0.6                                                          32.0 ˜     0.0                                                          ______________________________________                                    

It was confirmed that the granules 111 having the size distribution asshown in Table 4 were substantially identical with the wood meal 102 ofthe size distribution as shown in Table 3 in its mean particle size,except that the size was slightly smaller and the bulking densityincreased.

In other words, whereas the bulking density of the wood meal 102 shownin Table 3 ranged between 0.126 g/cc when not packed and 0.286 g/cc whenpacked, that of the granules 111 shown in Table 4 ranged between 0.186g/cc when not packed and 0.463 g/cc when packed, indicating that thebulking density of the granules 111 was significantly increased.

The bulking density of the granules when not packed here means a valuewhich is measured by sifting said granules 111 with a 24 mesh sieve in a100 cc vessel to overflowing, levelling off the heap to measure thetotal weight of the granules contained in the vessel, and dividing theweight by 100. The bulking density of granules when packed is measuredby sifting said granules 111 with a 24 mesh sieve into a 100 cc vesselunder vertical vibration (tapping vibration) until the bulk of thegranules inside the vessel ceases to change despite said vibration,levelling off the heap, and dividing the total weight of the granules111 by 100.

The wood meal 102 which is shown in Table 3 and which is not subjectedto pulverization includes elongated granules in which one elliptic axisis longer than the other, or with rugged or protruding portions andvilus-like fibers. On the other hand, microscopic observation confirmedthat granules 111 shown in Table 4 were generally more well shaped witha relatively smooth surface well covered with the fine particles.

The granules 111 thus obtained hardly become coagulated with oneanother, and are therefore suitable as a matrix for supporting pigmentsbecause of excellent dispersing performance in a solution and the like.

Experimental Example A-II

Chips of black spruce which is the same as the wood material 101 used inthe example mentioned above were used, which were subjected to crushingby the same impeller mill as used in Experimental Example A-I in whichthe clearance between the impellers of the rotor and the liner was setat 3 mm, to obtain treated wood meal 102 having the particle sizedistribution shown in Table 2.

The wood meal 102 thus crushed was charged in a 5.4 liter ball millcontaining 2.4 liters of 3 mmφ ceramic balls of zirconium base andsubjected to pulverization for two hours to obtain the granules 111having the size distribution as shown in Table 5. Using a device for airclassification (PS Separator manufactured by Pautech K. K.), thegranules were classified to obtain the granules 111 having the sizedistribution as shown in Table 6.

                  TABLE 5                                                         ______________________________________                                        Particle Size (μm)                                                                      Amount of Distribution (wt %)                                    ______________________________________                                        ˜  0.2     0.0                                                          0.2 ˜                                                                            0.4     0.3                                                          0.4 ˜                                                                            0.6     0.4                                                          0.6 ˜                                                                            0.8     0.5                                                          0.8 ˜                                                                            1.0     0.8                                                          1.0 ˜                                                                            1.5     2.1                                                          1.5 ˜                                                                            2.0     3.6                                                          2.0 ˜                                                                            3.0     6.9                                                          3.0 ˜                                                                            4.0     6.0                                                          4.0 ˜                                                                            6.0     8.6                                                          6.0 ˜                                                                            8.0     10.5                                                         8.0 ˜                                                                            12.0    16.8                                                         12.0 ˜                                                                           16.0    13.0                                                         16.0 ˜                                                                           24.0    16.8                                                         24.0 ˜                                                                           32.0    9.1                                                          32.0 ˜                                                                           48.0    4.6                                                          48.0 ˜     0.0                                                          ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        Particle size (μm)                                                                      Amount of Distribution (wt %)                                    ______________________________________                                        ˜  0.2     0.0                                                          0.2 ˜                                                                            0.4     0.3                                                          0.4 ˜                                                                            0.6     0.5                                                          0.6 ˜                                                                            0.8     0.7                                                          0.8 ˜                                                                            1.0     0.9                                                          1.0 ˜                                                                            1.5     2.4                                                          1.5 ˜                                                                            2.0     5.2                                                          2.0 ˜                                                                            3.0     15.8                                                         3.0 ˜                                                                            4.0     18.8                                                         4.0 ˜                                                                            6.0     22.1                                                         6.0 ˜                                                                            8.0     14.8                                                         8.0 ˜                                                                            12.0    10.6                                                         12.0 ˜                                                                           16.0    5.2                                                          16.0 ˜                                                                           24.0    2.3                                                          24.0 ˜                                                                           32.0    0.4                                                          32.0 ˜     0.0                                                          ______________________________________                                    

Microscopic photographs of the granules confirmed that the majority ofthe resultant granules 111 were well shaped, had smooth surface and werewell covered with the fine particles.

Further, since the size distribution was limited within a relativelynarrow range, the granules had higher flowability and dispersingperformance and were suitable as a matrix for supporting pigments andthe like.

Comparative Example A-III

Chips of black spruce having the particle distribution as shown in Table1 were crushed in a 5.4 liter ball mill (Atritor A-200 by Mitsui MiikeKakouki K. K.) containing 2.4 liters of 3 mmφ ceramic balls of zirconiumbase for two hours.

The wood meal thus obtained contained both ultra-fine particles andelongated fibrous particles. More than 70 wt % of the particles remainedsubstantially uncrushed, and not all particles were shaped as a regulargranule.

When compared with the Experimental Examples wherein the spruce chipsare crushed and then pulverized with a frictional means to increase thebulking density, the granules of the Comparative Example that areobtained by directly pulverizing the chips are uneven in the particlesize distribution and defectively contain both ultra-fine particles andelongated fibrous particles.

The over-pulverized wood meal became coagulated and was not suitable forpractical use.

Fixing Fine Particles on the 1st Wood Meal Surface

Details regarding fixing of smaller and harder particles 112 on thesurface of the granules 111 to manufacture the first wood meal 110 willnow be described.

The particle size of the granules 111 is preferably as uniform aspossible. In other words, when the granules 111 are to be added in acoating solution, the size distribution of the major portion of thegranules is preferably within the range of from 2 to 12 μm.

In the case the granules 111 are to be added to a resincoating solutionor a resin material for molding plastic sheets and films, the particlesize is preferably smaller than 32 μm, and more preferably smaller than20 μm. Still more preferably, particles having the size smaller than 12μm account for more than 75 wt % of the total granules, and preferablymore than 80 wt % thereof.

When the granules are to be added in plastic products obtained byinjection or extrusion molding, the granules 111 are preferably in thesize distribution ranging from 50 to 90 μm, and more preferably smallerthan 200 μm.

When the granules are to be blended and mixed in plastic sheets and thelike obtained by molding with calendar rolls, the granules 111 may havea particle size larger than the size of the particles that are blendedin the resin material for molding other types of products.

As for fixing of the fine particles 112 on the surface of the granules111 utilizing the external pressing force, it is possible to use varioustypes of mixing devices capable of crushing or exerting externalpressing force on the surface of the granules 111 with increase bulkingdensity via the fine particles.

Here, the fine particles 112 bite into the surface of the granules 111and become fixed thereon. As the particles 112 bite into the granules111, heat is generated as plural particles press or rub with oneanother. Frictional heat is also generated by crushing of the granules.As a result, the fine particles 112 also become embraced by thegranules.

Entanglement among fine particles biting in the granules or betweenthose biting in the granules with those embraced by the granules alsoassures effective fixing of the particles on the granules, coupled bythe effect of slight shrinkage of the granules due to cooling aftercompletion of pulverization process. In other words, the fine particlescan be firmly fixed on the granules without resorting to chemicalreaction or adhesive.

Fine particles 112 and the granules 111 may be simultaneously charged ina device that can exert external pressing force on both, such as a dryball mill, to allow fixing of the particles on the granules.

The granules 111 may be sprinkled with the fine particles 112 inadvance. The granules 111 tentatively supporting the particles 112 maybe charged in a device such as a dry ball mill to cause the particles tobite into the granules by the external pressing force exerted by thedevice.

The granules 111 may be either completely or partly covered with thefine particles 112.

The fine particles 112 may be fixed in plural layers on the granulesurface.

Fixing Fine Particles on the 2nd Wood Meal

Details regarding fixing of smaller and harder particles 112 on thesurface of the granules 111 to manufacture the second wood meal 110 willnow be described.

Fine particles 122 are fixed on the granules 121 concurrently during theprocess of forming said granules 111 of the first wood meal 110. Devicesand means for forming the granules 121 and means for fixing the fineparticles are all identical with those employed in the case of the firstwood meal 110.

Raw material woods or chips are crushed with a cutter mill and thenfurther pulverized in an impeller mill to obtain treated wood meal 102having the particle size distributed within a given range. The treatedwood meal 102 and the fine particles 122 are charged in a pulverizersuch as a dry ball mill to simultaneously increase the bulking densityof the wood meal 102 and fix the particles on the surface of the treatedwood meal 102 or the granules 121 with increased bulking density.

Therefore, the fine particles 122 may be permanently or tentativelysprinkled on the surface of the wood meal while the bulking density ofthe wood meal is being increased, to be eventually fixed on the surfaceof the granules 121 with increased bulking density.

Alternatively, the fine particles 122 may become fixed on the surface ofthe granules with sufficiently increased bulking density 121 by theexternal pressing force exerted by the pulverization of the wood meal102.

In either case, the fine particles 122 become fixed on the granules 121having increased bulking density to obtain the second wood meal 120.

The fine particles 122 are fixed on the granule surface 121 of thesecond wood meal 120 in the same manner as in the case of the first woodmeal 110. The fine particles bite into the surface, are embraced by thesurface or are fixed by entanglement among those biting and thoseembraced by the granules.

If the second wood meal 120 as a final product is required to haveparticle size of uniform distribution, the treated wood meal 102 can besubjected to classification before the wood meal 102 is charged insidethe pulverizer together with the fine particles 122.

On the other hand, if the particle size distribution in the finalproduct need not be uniform, it is not necessary to classify thegranules.

The fine particles 122 may entirely or partly cover the surface of thetreated wood meal 102 or wood meal granules 121.

The fine particles 122 may also form layers on the surface of the woodmeal 102 or the granules 121.

Fine Particles

Fine particles 112, 122 to be fixed on the surface of the wood meal 111,121 will be described.

The fine particles 112, 122 may include various types of pigments,inorganic substances, metals, plastics and electroconductive substances.The fine particles 112, 122 are such that they have the size andhardness sufficient to bite into the surface of the wood meal 111, 121(and the treated wood meal 102 in the second and the fourth inventions).

The fine particles 112, 122 having the appropriate properties areselected to suit the use of the wood meal 110, 120.

Generally, when the wood meal 110, 120 is to be blended in the plasticmaterial for molding plastic products or in coatings, the fine particles112, 122 are preferably those which are chemically and thermally stable,which would not become deteriorated during use, or which would give noadverse effect on the molded plastic products or the coated layer.

Wood Meal Containing Inorganic Particles

Wood meal 110, 120 obtained by fixing inorganic particles 112, 122 onthe surface of granules 121 will now be described.

Inorganic substances to be used as the fine particles 112, 122 should beharder than the wood meal granules 111, 121 or the treated wood meal102, and yet should be smaller than the size of the granules 111, 121 orthe wood meal 102. Inorganic substances must also be compatible with thesubstances to which they are blended or with the conditions of use.

The particle size of the granules 111, 121 (in this case treated woodmeal 102) on which the inorganic substance, typically such as finepowder of calcium carbonate, is fixed is preferably arranged within agiven distribution, considering the purposes and mode of use of woodmeal 110, 120 such as whether it is blended in plastic sheets, plasticboards or other various moldings obtained by such methods as extrusionmolding and injection molding coating, or roll forming.

When the wood meal is to be blended in plastic film or sheet, thegranules 111, or the treated wood meal 102 in the case of the secondwood meal 120 should preferably have a particle size of smaller than 32μm, and more preferably smaller than 20 μm. The particle sizedistribution is more preferably such that more than 75 wt % and morepreferably more than 80 wt % of the wood meal measures 12 μm or smaller.

When the wood meal is to be blended in plastic products obtained byinjection or extrusion molding, the granules 111, or the treated woodmeal 102 in the case of the second wood meal 120 should preferably havea particle size of from 50 to 90 μm, and more particularly smaller than200 μm.

When the wood meal is to be blended in plastic sheets obtained by amolder such as a calendar roll in which the starting materials arekneaded, wood meal having a still larger particle size can be used.

Inorganic substances such as calcium carbonate powder may be fixed onthe surface of the granules 111, 121 or the treated wood meal 102 inexactly the same manner as in the case of the first or the second woodmeal 110 or 120 mentioned above.

Inorganic particles are fixed on the surface of the matrix granules 111,121 as they bite thereinto to preferably cover the entire surface.

The wood meal 110, 120 thus obtained gave size stability to plasticboards and the like, with little expansion or contraction due totemperature changes.

Details of fixing fine powder of calcium carbonate as the fine particles112, 122 onto the surface of the granules 111, 121 and the treated woodmeal 102 to obtain the wood meal 110, 120 will now be describedreferring to experimental examples. (To facilitate understanding of theexperimental examples, the same reference numbers are used to denoteitems that are the same as those in the foregoing examples, such as theraw material 101, the treated wood meal 102, granules 111, 121, and woodmeal 110, 120.)

Experimental Example B-I

Chips of black spruce having the particle distribution as shown in Table1 were used as the raw material 101, which were subjected to mechanicalcrushing by the impact, shear or friction forces of an impeller mill(Model IMP-250 by Seishin Kigyo K. K.) in which the clearance betweenthe impellers of the high speed rotor and the liner was set at 3 mm, toobtain treated wood meal 102 having the particle size distribution asshown in Table 2 above.

The wood meal 102 thus crushed was classified to obtain the particlesize distribution as shown in Table 3.

The wood meal 102 thus crushed and classified was charged in a 5.4 litercapacity dry type ball mill (Atritor A-200 by Mitsui Miike Kakouki K.K.) containing 2.4 liters of 3 mmφ ceramic balls of zirconium base andsubjected to pulverization for two hours to obtain wood meal granules111 with increased bulking density having the size distribution as shownin Table 4.

The granules 111 thus obtained and weighing 1.5 kg were sprinkled with1.5 kg of fine particles of calcium carbonate, charged in a dry ballmill (Atritor A-200 by Mitsui Miike Kakouki K. K.) and mixed to obtainthe wood meal 110 covered with the fine particles of calcium carbonateas intended.

Using the wood meal 110 thus obtained as a filler, PVC sheets wereprepared.

The PVC sheets contained said wood meal 110 uniformly distributedtherein, had no sticky feel on the sheet surface, and showed very littleexpansion or contraction due to temperature changes.

Experimental Example B-II

Wood chips were crushed using an impeller mill (Model IMP-250 by SeishinKigyo K. K.) to obtain treated wood meal 102 having the particle sizedistribution as shown in Table 7.

The treated wood meal 102 weighing 1 kg was sprinkled with 0.7 kg offine particles 122 of calcium carbonate, charged in a dry ball mill(Atritor A-200 by Mitsui Miike Kakouki K. K.) for pulverization for twohours.

The surface of the treated wood meal 102 was shaped and had the fineparticles of calcium carbonate biting and fixed thereon to obtain thewood meal 120.

The wood meal 120 thus obtained was used as a filler to manufacture PVCrods by extrusion molding.

The rod material thus obtained contained said wood meal 120 uniformlydistributed therein, had no sticky feel on the surface, and showed verylittle expansion or contraction due to temperature changes.

                  TABLE 7                                                         ______________________________________                                        Particle Size (μm)                                                                      Amount of Distribution (wt %)                                    ______________________________________                                        ˜  0.2     0.0                                                          0.2 ˜                                                                            0.4     0.1                                                          0.4 ˜                                                                            0.6     0.1                                                          0.6 ˜                                                                            0.8     0.1                                                          0.8 ˜                                                                            1.0     0.1                                                          1.0 ˜                                                                            1.5     0.3                                                          1.5 ˜                                                                            2.0     0.6                                                          2.0 ˜                                                                            3.0     0.9                                                          3.0 ˜                                                                            4.0     0.7                                                          4.0 ˜                                                                            6.0     1.2                                                          6.0 ˜                                                                            8.0     1.8                                                          8.0 ˜                                                                            12.0    2.6                                                          12.0 ˜                                                                           16.0    3.3                                                          16.0 ˜                                                                           24.0    6.2                                                          24.0 ˜                                                                           32.0    6.7                                                          32.0 ˜                                                                           48.0    8.4                                                          48.0 ˜                                                                           64.0    13.5                                                         64.0 ˜                                                                           96.0    32.6                                                         96.0 ˜                                                                           128.0   18.1                                                         128.0 ˜                                                                          192.0   2.7                                                          ______________________________________                                    

Wood Meal Containing Particles of Pigment

Particles of pigments to be used as the fine particles 112, 122 and thewood meal granules 111, 121 fixed with the fine particles to provide thewood meal 110, 120 will now be described.

Any type of pigments, inorganic or organic, can be used as the fineparticles 112, 122 so long as they are harder than the granules 111, 121and the treated wood meal 102, they are smaller than the size of thegranules, and they are compatible with the substances to which they areblended or with the conditions of user such as heat resistance.

It is preferable that the granules 111, 121 (in this case the treatedwood meal 102) which support the pigment particles are as uniform inparticle size as possible.

When the wood meal is to be blended in a coating material, the majorportion of the granules 111 or the treated wood meal 102 of the secondwood meal 102 preferably has a particle size distribution in the rangeof from 2 to 12 μm.

When the wood meal is to be blended in a coating material, or plasticproducts such as film or sheet, the size distribution is preferably inthe range of 32 μm or smaller. It is preferable to classify the woodmeal into the size distribution of 20 μm or smaller. More preferably,more than 75 wt % and still more preferably more than 80 wt % of thewood meal is smaller than 12 μm.

When the wood meal is to be blended in plastic products obtained byinjection or extrusion molding, the size distribution is preferably inthe range of from 50 to 90 μm, and more preferably smaller than 200 μm.

When the wood meal is to be blended in plastic sheets obtained by amolder such as a calendar in which the starting materials are kneaded,wood meal having a still larger particle size can be used.

The granules 111, 121 and the treated wood meal 120 are covered with thefine particles 112, 122 of pigments in the same manner as in theexamples mentioned earlier.

The fine particles of pigments preferably cover the entire surface ofthe granules or wood meal by biting thereinto.

Amount of fine particles 112, 121 to be blended may arbitrarilydetermined depending on the desired coloring of the final product. Thewood meal 110, 120 was found to have a good flowability and color whichwas substantially the same as the color of the pigment blended.

In the injection and extrusion molding of a material blended with thewood meal 110, 120 covered with the fine particles of pigment, the moldpressure was low in either cases and the molded products contained thepigments uniformly dispersed therein. No uneven coloring was observed.

Details of fixing fine power of pigment as the fine particles 112, 122onto the surface of the granules 111, 121 and the treated wood meal 102to obtain the wood meal 110, 120 will now be described referring toexperimental examples. (To facilitate understanding of the experimentalexamples, the same reference numbers are used to denote items that arethe same as those in the foregoing embodiments, such as the raw material101, the treated wood meal 102, granule 111, 121, and wood meal 110,120.)

Experimental Example C-I

Chips of black spruce having the particle size distribution as shown inTable 1 were used as the raw material 101, which were subjected tomechanical crushing by a crushing means utilizing impact or crushingforces such as an impeller mill (Model IMP-250 by Seishin Kigyo K. K.)in which the clearance between the impellers of the high speed rotor andthe liner was set at 3 mm, to obtain treated wood meal 102 having theparticle size distribution as shown in Table 2.

The treated wood meal 102 thus obtained was classified into the sizedistribution as shown in Table 3.

The wood meal 102 thus classified was charged in a 5.4 liter capacitydry ball mill (Atritor A-200 by Mitsui Miike Kakouki K. K.) with 2.4liters of 3 mmφ ceramic balls of zirconium base for pulverization fortwo hours to obtain granules 111 with increased bulking density and thesize distribution as shown in Table 4.

The granules 111 thus obtained and weighing 1 kg was sprinkled with 0.7kg of the fine particles of titanium oxide, and the fine particles oftitanium oxide were fixed on the surface of the granules 111 using thesame ball mill as mentioned above to obtain wood meal 110.

Microscopic photographs of the granules confirmed that the titaniumoxide particles were supported on the matrix granules 111 as thetitanium oxide particles bit into the surface of the granules. The woodmeal 110 as a whole was generally white in color, which is the originalcolor Of the titanium oxide. The flowability and the dispersionperformance in solutions were both excellent. Plastic boards added withthe granules 110 as the pigment showed very little expansion orcontraction due to temperature changes.

Experimental Example C-II

Wood chips were pulverized using an impeller mill (Model IMP-250 bySeishin Kigyo K. K.) to obtain treated wood meal 102 having the particlesize distribution as shown in Table 7. The wood meal 102 weighing 1.5 kgwas covered with 1.5 kg of fine particles 122 of titanium oxide andcharged into a dry ball mill (Atritor A-200 by Mitsui Miike Kakouki K.K.) for pulverization for two hours.

As pulverization with the ball mill proceeded, rugged or protrudingportions as well as vilus-like fibers of said treated wood meal 102 wereremoved to obtain wood meal granules 121 that were generally wellshaped.

The wood meal 120 thus obtained was found to have the fine particles oftitanium oxide firmly biting on the surface of the granules 121.

Using the wood meal 120 thus obtained as the pigment, plastic boardswere molded. The coloring of the resultant product was even and white.The board had no sticky feel on the surface, and showed little expansionor contraction due to temperature changes.

It is noted that because of the strong mechanical impact exerted by saidpulverization, biting of fine particles 112, 122 of the pigment into thematrix granules 111, 121 and the treated wood meal 102 is enhanced. Anadditional experiment was conducted using a ball mill provided withimpellers that are arranged vertically to have the fine particles 112,122 of pigments fixed on the surface of the treated wood meal 102 andgranules 111 under friction and impact of dropping. The resultant woodmeal 110, 120 had brilliant color.

Wood Meal With Fine Particles of Electroconductive Substance

The wood meal 110, 120 obtained by fixing fine particles 112, 122 ofelectroconductive substance on the surface of the granules 111, 121 willnow be described.

As mentioned earlier, any electromagnetic substances may be used so longas the particles thereof are harder than the granules 111, 121, and thetreated wood meal 102, they have smaller particle size than the size ofsaid granules or wood meal, and they are compatible with the substancesto which they are blended or with the conditions of use such as heatresistance.

Such electroconductive substances include electroconductive metals suchas Ag, Cu and Ni, metallic oxides such as SnO₂ and ZnO, and carbon basedsubstances. One or more of such substances may be selectively used.

The wood meal 111, 120 comprising the granules 111, 121 and the treatedwood meal 102 with the fine particles of electroconductive substancebiting on the surface thereof can be dispersed in coating solutions tobe used as an electroconductive filler for shielding or absorbingelectromagnetic wave, or preventing electrostatic charging.

It is preferable that the granules 111, 121 (in this case in the form oftreated wood meal 102) which support the electroconductive particleshave as uniform a particle size as possible.

For example, the major portion of the granules 111, or treated wood meal102 for the second wood meal 120 is preferably within the particle sizedistribution of from 2 to 12 μm. It is also preferable that the granules111, or the treated wood meal 102 for the second wood meal 120 have theparticle size distribution of 32 μm or smaller, and more preferablysmaller than 20 μm. Still more preferably, more than 75 wt %, morepreferably more than 80 wt % of the granules is smaller than 12 μm insize.

The granules 111, 121 and the treated wood meal 120 are covered withfine particles 112, 122 of electroconductive substance in the samemanner as in the examples mentioned above. The fine particles preferablycover the entire surface of the granules or wood meal by bitingthereinto. The wood meal 110, 120 supporting the electroconductiveparticles was found to have excellent flowability and dispersionperformance.

Amount of fine particles to be fixed on the granules 111, 121 may beselected suitably to achieve required level of conductivity. Basically,the electroconductive particles must be in electric connection with oneanother, and the amount may be increased to achieve the required levelof electric conductivity.

Details of fixing the electroconductive particles 112, 122 onto thesurface of the granules 111, 121 and the treated wood meal 102 to obtainthe wood meal 110, 120 will now be described referring to experimentalexamples and comparative examples. (To facilitate understanding of theexperimental examples, the same reference numbers are used to denoteitems that are the same as those in the foregoing examples, such as theraw material 101, the treated wood meal 102, granule 111, 121 and thewood meal 110, 120.)

Experimental Example D-I

Chips of black spruce having the particle distribution as shown in Table1 were used as the raw material 101, which were subjected to crushing byan impeller mill (Model IMP-250 by Seishin Kigyo K. K.) in which theclearance between the impellets of the high speed rotor and the linerwas set at 3 mm, to obtain treated wood meal 102 having the particlesize distribution as shown in Table 2.

The treated wood meal 102 thus obtained was classified into the sizedistribution as shown in Table 3.

The wood meal 102 thus classified was charged in a 5.4 liter capacitydry ball mill (Atritor A-200 by Mitsui Miike Kakouki K. K.) with 2.4liters of 3 mmφ ceramic balls of zirconium base for pulverization fortwo hours to obtain granules 111 having increased bulking density andthe size distribution as shown in Table 4.

Fine particles of carbon measuring 50 parts by weight were sprinkled tocover the entire surface of the granules 111 measuring 100 parts byweight and were fixed using the same ball mill as mentioned above.

A solution was prepared by combining 60 parts by weight of a solventcontaining dimethylformamide and methylethyl ketone at the ratio of 1:1and 20 parts by weight of urethane resin.

The solid content of urethane resin in the solution and the wood meal110 fixed with carbon particles on the surface were mixed at the ratioof 1:1 and kneaded in a ball mill for about 10 minutes to obtain anelectroconductive coating material.

The resultant electroconductive coating material was used to form a filmlayer of about 21 μm thickness. The electric resistance on the surfaceof the film was measured to be between 1×10⁷ to 1×10⁸ ohm, indicatingthat excellent conductivity is obtained.

The solid content of urethane resin in the solution and the wood meal110 fixed with carbon particles on the surface were mixed at the ratioof 1:2 in weight and kneaded in a ball mill for about 10 minutes toobtain an electroconductive coating material.

The resultant electroconductive coating material was used to form a filmlayer of about 28 μm thickness. The electric resistance measured on thesurface of the film indicated that the film had betterelectroconductivity than the film obtained by using theelectroconductive coating material mentioned above.

Experimental Example D-II

The raw material wood 101 was crushed in the same manner as in ExampleD-I to obtain the treated wood meal 102 having the particle sizedistribution as shown in Table 2. The resultant wood meal 102 wasclassified to have the size distribution as shown in Table 3.

The treated wood meal 102 weighing 2 kg was sprinkled with carbonparticles 122 weighing 1 kg, and then charged in a dry ball mill(Atritor A-200 by Mitsui Miike Kakouki K. K.) for pulverization for twohours to obtain the wood meal 120.

The surface of the wood meal 120 thus obtained was well shaped and thebulking density was increased. The carbon particles were found to havebitten into the surface.

A coating film layer was formed using a coating material containing thewood meal 120 as a filler. The electric resistance measured on the filmlayer indicated that the electroconductivity comparable to that obtainedin Example D-I was obtained.

Comparative Example D-III

To 100 parts by weight of 30% urethane resin solution were added 30parts by weight of carbon particles, and the mixture was kneaded in aball mill for about 10 minutes to obtain an electroconductive coatingmaterial.

A coating film layer of 21 μm thickness was formed using theelectroconductive material. The electric resistance was measured to be1×10⁹ ohm at any portion of the surface. The carbon particles wereobserved to have coagulated within the film layer.

Mixing and kneading of the urethane resin and the carbon particles wascontinued until the electric resistance of the film layer of 1×10⁸ ohmor lower was achieved.

The electric resistance of the film surface was measured at the end ofeach kneading period. It was not until the kneading was continued for 40to 50 hours in the ball mill that the electric resistance reached 1×10⁸ohm.

Comparative Example D-IV

The raw material wood 101 was crushed in the same manner as in ExampleD-I to obtain the treated wood meal 102 having the particle sizedistribution as shown in Table 2. The resultant wood meal 102 wasclassified to have the size distribution as shown in Table 3.

The wood meal 102 thus classified was charged in a 5.4 liter capacitydry ball mill (Atritor A-200 by Mitsui Miike Kakouki K. K.) with 2.4liters of 3 mmφ ceramic balls of zirconium base for pulverization fortwo hours to obtain granules 111 having the particle size distributionas shown in Table 4.

Dimethylformamide and methylethyl ketone were blended at the ratio of1:1 to prepare a solvent, which was used to dilute and prepare 25%urethane resin solution. The urethane resin solution was added with thegranules 111 and carbon particles in such amounts that the weight ratioof the granules, carbon particles and the solid content of the urethaneresin would be 2:1:3. The mixture was kneaded in a ball mill for about10 minutes to obtain an electroconductive coating material.

A film layer of about 21 μm thickness was formed using theelectroconductive coating material. The electric resistance was measuredto be 1×10⁹ ohm at any portion of the surface. The carbon particles wereobserved to have coagulated within the film layer.

Mixing and kneading of the urethane resin and the carbon particles wascontinued until the electric resistance of the film layer of 1×10⁸ ohmor lower was achieved.

The electric resistance of the film surface was measured at the end ofeach kneading period. It was not until the kneading was continued forabout 40 hours in the ball mill that the electric resistance reached1×10⁸ ohm.

Comparative Example D-V

An electroconductive coating material was obtained in the same manner asin Comparative Example D-IV except that the granules 111 of ComparativeExample D-IV, carbon particles and the solid content of the urethaneresin were mixed at the weight ratio of 4:2:3.

A film layer of about 28 μm thickness was formed. The electricresistance was measured to be 1×10⁹ ohm at any portion of the surface.The carbon particles were observed to have coagulated within the filmlayer.

Wood Meal Fixed with Fine Particles of Other Types and Having DifferentProperties

The examples mentioned above indicate that inorganic substances,pigments, electroconductive substances and metals are advantageouslyused as the fine particles 112, 122 to be fixed on the granules 111, 121and the treated wood meal 102.

As is evident from the foregoing, the present invention includes use ofparticles of substances other than inorganic substances, pigments,electroconductive substances and metallic substances as the fineparticles 112, 122.

In other words, any particles that are harder and smaller than thegranules 111, 121 with increased bulking density and the treated woodmeal 102 may be used such as plastic particles as the fine particles112, 122 to be fixed either on the surface of the granules 121 or thetreated wood meal 102.

The wood meal 110, 120 may simultaneously function as anelectroconductive material as well as a coloring agent. This can beachieved by fixing particles of pigment and electroconductive materialon the surface of the granules 111, 121.

To obtain the wood meal 110, 120 with multiple functions, plural typesof fine particles 112, 122 each having respective functions are selectedand blended at a ratio that will give the required functions effectivelyto the final products.

What is claimed is:
 1. A method for making wood meal comprising thesteps of:a) providing raw material wood; b) crushing the raw materialwood into treated wood meal; c) pulverizing the treated wood meal intowood meal granules by the frictional forces of a plurality of balls in aball mill such that the wood meal granules have substantially roundedshape without rugged edges and without elongated protruding portions,thereby increasing the bulking density of the treated wood meal; d)providing a plurality of particles that are smaller and harder than thewood meal granules; and e) fixing the plurality of particles to thesurfaces of the wood meal granules in the ball mill such that theplurality of particles are forced into the surfaces of the wood mealgranules.
 2. A method as in claim 1, whereinsaid plurality of particlescomprise a pigment.
 3. A method as in claim 1, whereinsaid plurality ofparticles comprise an electroconductive material.
 4. A method as inclaim 1, whereinsaid plurality of particles are selected from the groupconsisting of inorganic and plastic materials.
 5. A method as in claim1, whereinsaid plurality of particles comprise at least any two ofinorganic materials and plastic materials.
 6. A method as in claim 1,wherein said ball mill is an open-type dry ball mill.
 7. A method as inclaim 1, wherein said ball mill is a closed-type dry ball mill.
 8. Amethod as in claim 1, and further comprising the step of classifying thetreated wood meal to obtain a uniform particle size distribution priorto said step of pulverizing.
 9. A method as in claim 1, wherein saidstep of fixing is implemented by charging the plurality of particlesinto the ball mill containing the wood meal granules.
 10. A method as inclaim 1, wherein said step of fixing further comprises the steps ofsprinkling the plurality of particles on the wood meal granules andcharging the resulting mixture in the ball mill.
 11. A method as inclaim 1, and further comprising the step of drying the treated wood mealto less than 10 wt. % moisture prior to said pulverizing step.
 12. Amethod, as in claim 1, wherein said pulverizing step is performed at atemperature below 80° C.
 13. A method, as in claim 1, wherein said ballshave diameters in the range of 3-15 mm.
 14. A method for making woodmeal comprising the steps of:a) providing raw material wood; b) crushingthe raw material wood into treated wood meal; c) providing a pluralityof particles that are smaller and harder than the treated wood meal; d)charging the treated wood meal and the plurality of particles into aball mill; e) pulverizing the heated wood meal into wood meal granulesby the frictional forces of a plurality of balls in the ball mill suchthat the wood meal granules have substantially rounded shape withoutrugged edges and without elongated protruding portions, therebyincreasing the bulking density of the treated wood meal; and f)simultaneously fixing the plurality of particles to the surfaces of thewood meal granules in the ball mill such that the plurality of particlesare forced into the surfaces of the wood meal granules.
 15. A method asin claim 14, whereinsaid plurality of particles comprise a pigment. 16.A method as in claim 14, whereinsaid plurality of particles comprise anelectroconductive material.
 17. A method for making wood meal comprisingthe steps of:a) providing raw material wood; b) crushing the rawmaterial wood into treated wood meal; c) providing a plurality ofparticles that are smaller and harder than the treated wood meal; d)mixing the treated wood meal with the plurality of particles andcharging the mixture in a ball mill; e) pulverizing the treated woodmeal into wood meal granules in the ball mill by the frictional forcesof a plurality of balls in the ball mill such that the wood mealgranules have substantially rounded shape without rugged edges andwithout elongated protruding portions, thereby increasing the bulkingdensity of the treated wood meal; and f) simultaneously fixing theplurality of particles to the surfaces of the wood meal granules in theball mill such that the plurality of particles are forced into thesurfaces of the wood meal granules.
 18. A method as in claim 17,whereinsaid plurality of particles comprise a pigment.
 19. A method asin claim 17, whereinsaid plurality of particles comprise anelectroconductive material.
 20. A method as in claim 17, whereinsaidplurality of particles are selected from the group consisting ofinorganic materials and plastic materials.